Despite the introduction of combination chemotherapy and improved early diagnosis breast cancer remains the second leading cause of cancer death of women in the United States. A new approach to prevention and treatment is needed. The long term research goal is to investigate the molecular pathogenesis of breast cancer in order to develop new preventive and treatment strategies. The proposed research project is designed to provide for her a broad foundation in molecular biology by investigating how the differentiation agent, retinoic acid (RA) regulates breast cancer cell proliferation and apoptosis. This project will utilize the expertise of Fred Hutchinson Cancer Research Center to investigate what cell cycle regulatory pathways are controlled by RA through the epithelial specific retinoic acid receptor beta (RARbeta). A functional RARbeta gene has been introduced by retroviral transduction into four breast cancer lines which did not express RARbeta mRNA. Cellular proliferation was inhibited in all RARbeta transduced cells when treated with RA; certain cells underwent apoptosis. A nude mouse assay will demonstrate the ability of RARbeta and retinoids to prevent tumor growth and metastasis in vivo. Northern and Western blotting will be used to investigate the role of cyclins, cyclin dependent kinases, and cdk inhibitors to mediate growth arrest and apoptosis in RARbeta transduced breast cancer cells. An antisense approach and temperature sensitive mutants will be used to investigate whether RARbeta mediated apoptosis occurs though a p53 dependent or independent pathway. The role of bcl-2 overexpression in modulating RARE mediated apoptosis will be investigated by retroviral gene transfer. The relationship between c-Myc, estrogen dependence, and apoptosis will be explored by an antisense approach and with the use of an estrogen-dependent c-Myc/estrogen receptor chimera.